In recent years, an object tracing device and an object tracing system are put into practical use in a field of monitoring device with a video camera, in which the video camera is taking a moving picture at any time and when any suspicious object is identified, the video camera starts tracing the object and taking a video picture of it.
Among those, an object tracing system having a wide-angle video camera and a video camera with a telephoto lens is widely deployed. The wide-angle camera has a fixed picture angle. The camera with a telephoto lens has a movable picture angle in up, down, left and right directions (hereinafter, the movements are called ‘pan’ and ‘tilt’). The object tracing system equipped with two cameras having a different picture-taking angle is widely used because it does not require complicated structure such as of a high-powered zoom-lens and its control means.
In an example of the object tracing system, a wide-angle video camera takes a picture of relatively a wide area to be monitored, and when an object comes into the picture, a telephoto video camera is directed toward the invading object facing with the object and taking a picture of the object. A display part displays an enlarged picture of the object. With this type of conventional structure, a surveyor can judge whether the invading object is really a suspicious person or not by seeing the enlarged picture of the object displayed on the display part. The above conventional constitution is disclosed by Unexamined Japanese Patent Publication No. H11-69342.
However, with this type of conventional technology, there is a possibility that the system does not trace a truly suspicious object when a plurality of invading objects exists from the beginning in the picture of the area-to-be-monitored taken by the wide-angle video camera. With this type of system, when an invading object is identified in a wide-angle picture, the telephoto lens starts tracing the object taking a picture of the invading object. However, if another invading object comes into the area to be monitored after above process, there is also a possibility that the system does not trace a really suspicious object.